Fiber reinforced plastic flat plates

ABSTRACT

A fiber reinforced plastic (FRP) flat plate having no warps is continuously prepared by curing a continuous FRP plate molding material both top and back surfaces of which are covered with film-like sheetings by means of an ionizing radiation. In the process, the FRP molding material is continuously transported in lengthwise direction, and tensions are given to said film-like sheetings in both lengthwise and widthwise directions before and in the course of the irradiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. applicationU.S. Ser. No. 362,306, filed May 21, 1973, now U.S. Pat. No. 3,930,098,the subject matter of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a continuous process for preparing a fiberreinforced plastic (hereinafter referred to as FRP) flat plate by meansof curing with an ionizing radiation, preferably an electron beam.Particularly, this invention comprises irradiating with an ionizingradiation an FRP plate molding material both top and back surfaces ofwhich are covered with a film-like sheeting, characterized in that themolding material covered with the sheetings is continuously transportedand tensions are given to the covered sheetings in both lengthwise andwidthwise directions in the course of processing.

(2) Description of the Prior Art

Generally, FRP plates have been prepared by impregnating a thermosettingresin such as unsaturated polyester resin containing a curing catalystin glass fibers, and curing preferably by means of a hot press method.

The heat-curing process has also been applied to a continuous molding ofan FRP flat plate. However, the continuous heat-curing process hasserious defects in large curing strain such as warps and cracks inappearance and formation of bubbles owing to violent exothermic reactionupon curing. When the generation of heat of reaction is regulated tolower, curing takes several to several-ten minutes. Therefore, it isdifficult to continuously prepare an FRP flat plate more than 3 mm inthickness even by employing a large curing furnace. Furthermore, sincesuch curing process takes a considerable long period of time and aliquid resin impregnated in reinforcing fiber material is of fluidnature, it is difficult to keep an FRP molding material in uniform shapeand thickness until the impregnated resin is sufficiently cured.Therefore, the resulting product is inferior in mechanical properties tohot-pressed product.

It is known that FRP molding material in small size such as 24 × 12inches which had been pressed in discontinuously transported on aconveyer and irradiated with electron beam to form FRP plate, asreported in Society of plastics Engineerings Journal, April 1967, pages33 - 73. However, this process remains in an experimental scale and isnot commercially available, since the warps, creases and unevenness takeplace more or less on the cured FRP plate. Such defects in the course ofcuring are further enhanced when a continuous FRP molding material iscured continuously by means of an ionizing radiation such as electronbeam, since there was no useful means to maintain the FRP moldingmaterial flat and uniform in the course of irradiation. Therefore, it isclear that the continuous process by means of heat curing can not bechanged to a continuous process by means of a radiation curing,especially an electron beam curing, by simply replacing heating withirradiation.

It is easily understood by those skilled in the art that a simplereplacement of heating with irradiation in the continuous process bymeans of heat curing could not create the present invention in which acontinuous FRP flat plate without strains is advantageously prepared bymeans of an ionizing radiation.

In summary, the commercially feasible FRP flat plate could have beenprepared only by way of a hot press method. However, the hot pressmethod requires a discontinuous processing operation, a long period oftime for curing and cooling and a larger scale of the apparatus.Further, an FRP plate of continuous long size can not be obtained by thehot press method.

Incidentally, the conventional FRP flat plates having glossy surfaceshave been commercially prepared with a hot press equipped with pressingplates having smooth surfaces such as metal-plated surfaces. Owing tothe characteristics of the hot press, many problems in preparing an FRPplate are substantially eliminated, such as non-uniformity of resinmaterials, formation of bubbles, warps of the plate, rising of fibermaterials caused by elastic recovery thereof, sink caused by curingvolume contraction, unevenness of the surfaces of the like. Thisinvention advantageously eliminates the above-mentioned problems withoutemploying the conventional hot press and provides a continuous FRP flatplate which could not be prepared by the hot press method.

SUMMARY OF THE INVENTION

The present inventors have succeeded in continuously preparing an FRPflat plate with smooth and glossy surface and without strains such aswarps and cracks by means of an ionizing radiation. The process of thisinvention comprises irradiating with an ionizing radiation a continuousFRP molding material both top and back surfaces of which are coveredwith film-like sheetings, while the molding material covered with thesheetings is continuously transported in lengthwise direction andtensions are given to the covered sheetings in both lengthwise andwidthwise directions in the course of the processing.

An object of this invention is to provide a continuous high-speedprocess for preparing an FRP flat plate by means of an ionizingradiation according to the above-mentioned process.

Another object of this invention is to provide an FRP flat plate of along size and irrespective of thickness without strains such as warpsand with smooth surface, which is improved in mechanical properties andcan be cut in any desired length upon application.

A further object of this invention is to provide an apparatus forcontinuously preparing an FRP flat plate according to theabove-mentioned process.

The other objects of this invention will be made clear in thedescriptions of the specification and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows cross-section of an apparatus employed in this invention.

FIG. 2 shows plan view of the same apparatus.

FIGS. 3A-3D are illustrations of the clips for tenters which can beemployed in this invention.

FIG. 4 shows cross-section of the molding material covered withsheetings, wherein tension is given in widthwise direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A conventional molding material for FRP plate can be applied to theprocess of this invention. The FRP plate molding material comprises areinforcing fiber material impregnated with a liquid resin materialcurable by means of an ionizing radiation. A conventional filler and/oradditive can optionally be added to the curable liquid resin material.

The reinforcing fiber materials comprise a fiber material and typicallyinclude a synthetic fiber such as a polyamide fiber, a polyester fiber,a polymeric acrylonitrile fiber, a polymeric vinyl chloride fiber, apolymeric vinyl alcohol fiber; a semi-synthetic fiber such as a rayon; anatural fiber such as cotton and hemp; an inorganic fiber such as aglass fiber, an asbestos, a rock wool, a carbon fiber, a boron fiber, ametal fiber and a whisker. The fibers can be in the form of a yarn, aroving, a staple fiber, non-woven fabrics, a cloth or a combinationthereof. The reinforcing fiber materials may be employed in the range ofabout 3 - 97%, preferably about 5 - 80% by weight of the FRP platemolding materials.

The curable resin materials comprise a resin, the mixture of a resin anda copolymerizable monomer or a mixture thereof which can be crosslinkedand cured by means of an ionizing radiation. Such resin materialsinclude an unsaturated polyester resin such as polyethylene maleatephthalate, an unsaturated acrylic resin, a saturated acrylic resin, adiallyl phthalate resin, a 1,2-polybutadiene resin, a modified epoxyresin such as an acrylic-modified epoxy resin, a modified urethane resinsuch as an acrylic-modified urethane resin, and a mixture thereof.Usually, these resins are advantageously used as a mixture with acopolymerizable unsaturated monomer or monomers. The resin materials areemployed in liquid form in the range of about 1 - 97%, preferably 4 -95% by weight of the FRP plate molding materials. The liquid resinmaterials to be employed have generally a viscosity in the range ofabout 1 - 30 poise at a temperature at which impregnation in the fibermaterials is effected.

The fillers to be employed include inorganic filler materials in powderform such as calcium carbonate, gypsum, cement, silica, talc, kaoline,alumina, diatomaceous earth, calcium sulfite, glass powder, mica, glassbease, silicic glass baloon. The fillers may be employed in the range of0 to about 500 parts by weight of 100 parts of the curable resinmaterials to be used. The additives to be employed include a coloringmaterial, a releasing agent, a thickening agent, a curing catalyst, anaccelerator for curing, a stabilizer for ultraviolet rays and anantiflaming agent. These additives are generally added in the range of 0to about 15 parts by weight of 100 parts of the curable resin materials.In the case of an antiflaming agent, it may be added up to about 100parts by weight.

The FRP plate molding material is covered with two continuous film-likesheetings on both top and back surfaces of the molding material. Thefilm-like sheetings are employed for maintaining the shape and thicknessof the molding material by applying tensions to the sheetings as well astransporting of the molding material and preventing escape of the resinmaterials from the molding material. The film-like sheeting should notbe swelling or soluble with the curable resin material and is requiredto be durable to the tensions in both lengthwise and widthwisedirections. Such film-like sheetings include a poly (ethyleneterephthalate) film, a polyamide film, a cellophane film, a substratesuch as paper or aluminum foil laminated with polyethylene,polypropylene, polyvinyl alcohol or the like. The thickness of thesheeting is in the range of about 10 - 200 microns. The sheetings of thedifferent species and thickness can be employed in the top and backcoverings of the FRP molding materials.

The FRP plate molding materials covered with film-like sheetings can beprepared with a conventional impregnating machine or sheet moldingcompound machine. One can use an FRP molding material in continuous formon the market such as sheet molding compounds.

The typical mode of practice of this invention is given below byreferring to the attached drawings.

An FRP continuous molding material 9 covered with film-like sheetingsprepared by the molding material processing machine 1 is compressed withthe press rollers 2 and the thickness thereof is controlled. The tensionin lengthwise direction is given by the press rollers 2 and the draftrollers 6. While the continuous molding material is transported inlengthwise direction, the tension in widthwise direction is given bygradually expanding the distance between tenters positioned at the bothsides of the molding material, wherein the clips 3 of the tenters holdthe both edges of the film-like sheetings. Thus, the continuous moldingmaterial having smooth surfaces is passed under the scanner 4 of anelectron beam accelerator and cured. The resulting cured FRP flat plateis cut in a desired length with cutter 7.

A conventional clip-tenter or pin-tenter can be employed in thisapparatus. Any type of the tenters can be employed which can firmly holdthe edges of the covering sheetings and does not break the sheetings.The typical example of the clip is shown in FIGS. 3A-3D. The clips canhold the edges of the covering sheetings at a position either before orafter the press rollers 2. It is preferred that the press rollers 2 besituated near the irradiation area such as scanner.

Generally, the same degree of the tensions are applied to the coveringsheetings in lengthwise direction by the draft rollers 6 and inwidthwise direction by the clip-tenters 3. Thus, the compression inthicknesswise direction and the tensions by friction in both widthwiseand lengthwise directions are given to the FRP molding material coveredwith the film-like sheetings, as shown in FIG. 4. It has been neveranticipated that a rising owing to elastic recovery of fiber materialsand a sink owing to curing of resin materials can advantageously becontrolled by the mechanism of said compression and tensions by frictionapplied to the FRP molding material. Thus, the FRP molding material ismaintained as if it were compressed by a press and can be continuouslytransported and cured. Furthermore, this invention can advantageously beapplied to an FRP molding material about 3 meters in width, since saidcompression and tensions by friction are effective even when the widthof the covering sheetings is about 3 meters or more.

In applying the widthwise tension to the both edges of the coveringsheetings, it is preferred that the distance between the adjoining clipsis gradually made larger as the FRP molding material covered withsheetings is transported nearer to the irradiation area, so as to avoidthe strains of the covering sheetings. The clip mechanisms which havebeen employed in a bi-axial drawing of a thermoplastic film for givingthe widthwise molecular orientation thereto can advantageously beapplied as one of the means for controlling the above-mentioned distancebetween the clips.

After the irradiation, it is preferred that the widthwise tension istemporarily loosened after the irradiation in order to unfasten theclips and smoothly release the covering sheetings.

The tensions to be applied to the film-like sheetings both in lengthwiseand widthwise directions may be changed within a range of about 1 - 20Kg/mm² according to the species and thickness of the sheetings, forexample as shown below.

    ______________________________________                                                          General    Preferred                                                          range of   range of                                                           tensions   tensions                                         Species of sheeting                                                                             (Kg/mm.sup.2)                                                                            (Kg/mm.sup.2)                                    ______________________________________                                        poly(ethylene terephthalate)                                                                     1 - 10    3 - 6                                            6-polyamide (Nylon-6)                                                                            1 - 12    3 - 7                                            cellophane        1 - 5      2 - 4                                            polyamide laminated with                                                                        1 - 6      3 - 4                                            polyethylene                                                                  kraft paper laminated with                                                                       1 - 10    3 - 5                                            polyethylene                                                                  cellophane laminated with                                                                       1 - 6      3 - 5                                            polyethylene                                                                  aluminum foil laminated with                                                                    1 - 3      1.5 - 2.5                                        polyethylene                                                                  poly(ethylene terephthalate)                                                                    1 - 4      2 - 3                                            laminated with polyethylene                                                   kraft paper laminated with                                                                      1 - 5      3 - 4                                            aluminum foil                                                                 ______________________________________                                    

The ionizing radiations to be employed in this invention include α rays,β rays, γ rays, X rays, electron beam, neutron beam and a mixturethereof. Generally, an electron beam from an accelerator is preferablyemployed. It is preferred that the electron beam or β rays has an energyin the range of about 0.3 - 7.0 MeV and a dose rate of about 0.01 - 20Mrad/sec. The total dose of the electron beam or β rays is about 0.1 -50 Mrad and preferably about 1 - 10 Mrad. Whey γ rays, X rays, α rays orneutron beam is employed, the dose rate thereof is about 10² - 10⁸rad/hr, and the total dose thereof is about 10⁴ - 10⁸ rad and preferablyabout 10⁵ - 10⁷ rad. The curing of the molding material can be promotedby the use of heating or irradiation with ultra-violet light orultrasonic wave in addition to or after the irradiation with an ionizingradiation. Two or more irradiation sources can be employed from one orboth sides of the molding materials.

The main excellent effects obtained by this invention are summarizedbelow.

(1) An FRP flat plate having uniform thickness and smooth surfaces canbe continuously produced in a large quantity with a short period oftime.

(2) A continuous FRP flat plate of more than 3 mm in thickness up to thethickness which an ionizing radiation can penetrate and 3 meters or morein width can rapidly be obtained.

(3) An FRP flat plate having mechanical properties superior to aconventional hot-pressed FRP plate can be obtained.

This invention is further explained by the foregoing examples. However,this invention should not be limited by these examples, and the changesand modifications within the spirit and scope of this invention can beeffected. The quantities and parts in the examples are based on weightunless otherwise specified.

EXAMPLE 1

Seventy parts of the liquid resin material essentially consisting of 100parts unsaturated polyester resin, 100 parts calcium carbonate, 1.5parts magnesium oxide and 3.75 parts additionally added styrene wasimpregnated in 30 parts of glass fiber mat comprising glass fiber rovingchopped in 1 cm long. A sheet molding compound (SMC) of about 3 mm thickand about 4.5 Kg/m² was prepared by covering the impregnated glass fibermat with 50 microns thick poly(ethylene terephthalate) films on both topand back surfaces. Said unsaturated polyester resin comprises 30 partsstyrene and 70 parts condensation polymer of 0.5 mol maleic anhydride,0.5 mol phthalic anhydride and 1.1 mol ethylene glycol, with the acidvalue 50.

The resulting SMC was passed through press rollers and the thicknessthereof was adjusted. Then, the both edges of the covering films wereheld by the clips of the tenters. The SMC was transported at thevelocity of 1 m/min in lengthwise direction. The tensions of about 6Kg/mm² were given to the covering films in lengthwise direction by thedraft rollers and in widthwise direction by the clip-tenters. Thus, theSMC was maintained to show smooth surfaces, no creases and no warps onboth top and back surfaces. The SMC was cured with the total dose of 2.5Mrad electron beam obtained from the electron beam accelerator of 2 MeVand 1 mA. An FRP flat plate of about 3 mm thick having very glossysurfaces and no warps was continuously obtained.

For the comparison, the above Example 1 was repeated without giving thewidthwise tension. The resulting FRP flat plate showed warps, unevensurfaces and relief pattern of glass fibers on the top surface, and wasnot considered to be commercially feasible.

EXAMPLE 2

Sixty parts acrylic-modified epoxy resin was impregnated in 40 partsglass cloth. The resulting molding material of about 2 mm thick wascovered with 200 microns thick cellophane on both sides. Saidacrylic-modified epoxy resin was prepared by reacting 1000 gramsbisphenol type epoxy resin (Shell Epon No. 1001) with 170 gramsmethacrylic acid in the presence of triethyl amine and dissolving theresulting condensation polymer of acid value 12 in 1100 grams styrene.

The above-prepared SMC was processed in the same way as in Example 1with the transportation velocity of about 4 m/min, and cured by means of2 Mrad electron beam from an accelerator or 1.5 MeV and 5 mA. Thetensions of about 2 Kg/mm² were given in both lengthwise and widthwisedirections in the meantime.

An FRP clear flat plate of about 2 mm thick having very glossy surfacesand no warps was continuously obtained.

EXAMPLE 3

Eighty-five parts of unsaturated acrylic resin was impregnated in 15parts of polyvinyl alcohol cloth. The resulting molding material wascovered with the laminated films of 6-polyamide (Nylon-6) film (20microns) and polyethylene film (50 microns) on top and back surfaces.Said unsaturated acrylic resin by reacting 1.7 mol methacrylic acid withthe copolymer comprising 2.6 mol methyl methacrylate, 5.0 mol of ethylacrylate and 1.7 mol glycidyl methacrylate, and dissolving the resultingpolymer (45.6%) in the mixture of styrene (17.2%) and methylmethacrylate (37.2%).

The resulting SMC was processed as in Example 1 with transportationvelocity of about 1.2 m/min. When tensions of 10 Kg/mm² were given inboth lengthwise and widthwise directions, electron beam of 10 Mrad fromaccelerator of 2.5 MeV and 5 mA was irradiated to the SMC. An acrylicsemi-transparent FRP flat plate having smooth surfaces and no warps wascontinuously obtained.

EXAMPLE 4

Seventy-five parts of liquid saturated acrylic resin was impregnated in25 parts asbestos cloth. The resulting molding material was covered withthe films as in Example 3. Curing was effected as in Example 1 at thetransportation velocity of about 0.4 m/min with 12 Mrad electron beamfrom an accelerator of 2.0 MeV and 2 mA, while the tensions of 2 Kg/mm²were given in both lengthwise and widthwise directions. An acrylic FRPflat plate having smooth surfaces and no warps was continuouslyobtained.

Incidentally, the above liquid saturated acrylic resin is methylmethacrylate polymer syrup containing about 10% polymer and about 90%monomer, and is generally prepared by polymerizing methyl methacrylatein about 10% yield.

EXAMPLE 5

Fifty parts of acrylic-modified 1,2-polybutadiene resin was mixed with50 parts glass powder and was impregnated in 10 parts sisal fibers. Theresulting molding material was covered with kraft paper (60 g/m²)laminated with polyethylene film (35 microns) on the both surfaces. Saidmodified polybutadiene resin was prepared by reacting 100 gramsepoxylated 1,2-polybutadiene (molecular weight 1000) with 22 gramsacrylic acid in the presence of triethyl amine and dissolving theresulting polymer (80%) in methyl methacrylate (20%).

The resulting SMC was processed in the same way as in Example 1 at thetransportation velocity of about 8 m/min. The tensions of 5 Kg/mm² wereadded in both lengthwise and widthwise directions. Curing was effectedwith 3 Mrad electron beam from an accelerator of 2.5 MeV and 10 mA.

An FRP flat plate having smooth surfaces and no warps was continuouslyobtained.

EXAMPLE 6

Seventy-five parts of liquid resin material consisting of unsaturatedpolyester resin 100 parts, cement 50 parts, calcium carbonate powder 50parts, magnesium oxide 1.0 part and benzoyl peroxide 2 parts wasimpregnated in 25 parts of glass mat. The impregnated glass mat wascovered with the laminated films of cellophane (50 microns) andpolyethylene (50 microns) to prepare the SMC of about 3 cm thick and 45Kg/m².

The SMC was processed as in Example 1 with the transportation velocityof 3 m/min and tensions of 4 Kg/mm² were given in both lengthwise andwidthwise directions. Curing was effected with 8 Mrad electron beam froman accelerator of 2.5 MeV and 10 mA. FRP flat plate having very glossysmooth surfaces and no warps was continuously obtained.

EXAMPLE 7

The SMC employed in Example 6 was cured with a conventional hot press atthe pressure of 20 Kg/cm² at 130° C for 10 minutes and then at 100° Cfor 2 hours. The mechanical properties of the resulting FRP plate areshown below together with those of the product of Example 6.

    ______________________________________                                                           Hot-pressed                                                                              Product of                                      Testing            FRP plate  Example 6                                       ______________________________________                                        flexural strength (JIS-K-                                                                        18.0 - 19.9                                                                              21.0 - 24.0                                     6911)              Kg/mm.sup.2                                                                              Kg/mm.sup.2                                     flexural modulus (JIS-K-                                                                          870 - 1050                                                                              1150 - 1300                                     6911)              Kg/mm.sup.2                                                                              Kg/mm.sup.2                                     retension of flexural                                                         strength (after heating at                                                                        96 - 98%   103 - 105%                                     150° C for 24 hours)                                                       "                                                                         (after heating at 200° C for                                                               90 - 95%   101 - 110%                                     24 hours)                                                                     Barcol hardness (GYZJ-934-1)                                                                     42 - 45    50 - 53                                         Acetone extraction (for 16                                                                        3 - 8%    about 0%                                        hours using Sexhlet)                                                          ______________________________________                                    

Incidentally, the velocity of transporting the FRP molding material inlengthwise direction is within a velocity sufficient to cure the moldingmaterial by means of an ionizing radiation, and is easily determined bythose skilled in the art with reference to the species and dose rate ofan ionizing radiation, the irradiation area such as the scanner area ofan electron beam accelerator, and the like. It is considered that thevelocity up to about 50 meters/minute can generally be applied.

It should be understood that the film-like sheeting covering and givingtension to the molding material need not necessarily be removed. Underthe proper circumstances, the film-like sheeting may remain as alaminate on the molded FRP plate. Such laminates are disclosed, forexample, in U.S. Pat. No. 3,958,072, which is hereby incorporated byreference.

It will be obvious to those skilled in the art that various changes maybe made without departing from the scope of the invention and theinvention is not to be considered limited to what is described in thespecification.

What is claimed is:
 1. A process for continuously preparing a fiberreinforced plastic (FRP) flat plate having no warps, comprising:coveringwith film-like sheetings both the top and bottom surface of a continuousFRP flat plate molding material comprising a reinforcing fiber materialimpregnated with a liquid resin material curable by means of an ionizingradiation; continuously transporting the covered material in thelengthwise direction; irradiating the covered material as it is beingtransported by means of an ionizing radiation until said moldingmaterial is cured, said ionizing radiation being β-rays, electron beam,or mixtures thereof, wherein the dose rate is about 0.01-20 Mrad/secwith a total dose of about 0.1-50 Mrad; and applying tensions to thefilm-like sheeting covering the FRP molding material in both thelengthwise and the widthwise directions before and in the course of theirradiation, said tensions being in a degree sufficient to press andhold the molding material so as to maintain the thickness thereofuniform and the surfaces thereof smooth before and in the course ofradiation.
 2. A process according to claim 1, in which the tensions tobe applied to the film-like sheetings in both directions are in therange of about 1-20 Kg/mm².
 3. A process according to claim 1, in whichsaid ionizing radiation comprises a beam employed at a dose rate of0.01-20 Mrad/sec with a total dose of about 0.1-50 Mrad.
 4. A processaccording to claim 1 in which heating is employed after the irradiation.5. A process according to claim 1, in which the tension in the widthwisedirection is gradually increased as the FRP molding material coveredwith sheetings is transported nearer to the irradiation area.
 6. Aprocess according to claim 1, in which the widthwise tension istemporarily loosened after the irradiation.
 7. A fiber reinforcedplastic (FRP) flat plate laminated with a film-like sheeting, which isprepared according to the process of claim
 1. 8. An FRP laminateaccording to claim 7, in which the FRP plate molding material comprisesa reinforcing fiber material impregnated with a liquid resin materialcurable by means of an ionizing radiation.
 9. A fiber reinforced plastic(FRP) flat plate laminated with a film-like sheeting, which is preparedaccording to the process of claim
 1. 10. A process for continuouslypreparing a fiber reinforced plastic (FRP) flat plate having no warps,comprising:covering with film-like sheetings both the top and bottomsurface of a continuous FRP flat plate molding material comprising areinforcing fiber material impregnated with a liquid resin materialcurable by means of an ionizing radiation; continuously transporting thecovered material in the lengthwise direction; irradiating the coveredmaterial as it is being transported by means of an ionizing radiationuntil said molding material is cured, said ionizing radiation beingα-rays, γ-rays, X-rays, neutron beam or mixtures thereof wherein thedose rate is about 10² -10⁸ rad/hr with a total dose of about 10⁵ -10⁷rad; and applying tensions to the film-like sheeting covering the FRPmolding material in both the lengthwise and the widthwise directionsbefore and in the course of the irradiation, said tensions being in adegree sufficient to press and hold the molding material so as tomaintain the thickness thereof uniform and the surfaces thereof smoothbefore and in the course of radiation.
 11. A process according to claim10, in which the tensions to be applied to the film-like sheetings inboth directions are in the range of about 1-20 Kg/mm².
 12. A processaccording to Claim 10, in which heating is employed after theirradiation.
 13. A process according to claim 10, in which the tensionin the widthwise direction is gradually increased as the FRP moldingmaterial covered with sheetings is transported nearer to the irradiationarea.
 14. A process in accordance with claim 10, in which the widthwisetension is temporarily loosened after the irradiation.
 15. A fiberreinforced plastic (FRP) flat plate laminated with a film-like sheeting,which is prepared according to the process of claim 10.